The invention relates generally to semiconductor wafer etching and more specifically to an improved gas distribution plate which substantially reduces the nonuniformities in the etch process that occurs across the semiconductor wafer.
As is well known in the art, various semiconductor fabrication techniques require the selective removal of deposited metal and dielectric films and in the case of DRAM processing, the etching of deep trenches in the semiconductor wafer. Of late, the trend has been away from well known wet chemical etching processes and toward dry etching processes such as reactive ion etching and plasma etching. This is due in large part to the improved controllability and cost effectiveness imparted by the dry etching processes when compared with wet chemical etching processes.
Both reactive ion etching and plasma etching take place in a process chamber which is designed to process a single semiconductor wafer at a time. The semiconductor wafer is mounted on a wafer chuck which forms the bottom electrode of the process chamber. An upper electrode is located over the semiconductor wafer. The semiconductor wafer is bombarded by ions generated between the upper electrode spaced above the substrate and a lower electrode forming the substrate stage of the process chamber. An etchgas, which not only provides the source for the ions, but also improves the etch rate reactively, is transported to and distributed across the substrate via a gas distribution plate under a partial vacuum or a high vacuum. These operational pressures are dependent upon whether the process is reactive ion etching or plasma etching.
In single wafer systems, pressure differences and differences in the etchgas/etch product mixture can lead to etching nonuniformities across the surface of the substrate, especially from the center of the substrate to the edge of the substrate. The nonuniformities become more severe as the diameter of the substrate increases, particularly when the substrate approaches or exceeds 300 mm in diameter. Such nonuniformities of film deposition or etching can lead to various problems. For example, in the manufacture of semiconductors and integrated circuits, such nonuniformities can result in devices that do not function or function with less than optimal results.
The prior art has provided various solutions to the problem of nonuniform etching of the substrate. One such solution is to utilize different gas distribution plates for different diameter substrates or focus rings to compensate for the nonuniformities of the etching process. A disadvantage to this approach is that finding the correct gas distribution plate or focus ring can be very time consuming and thus costly. In addition, the appropriate gas distribution plate for a particular etching process may not be appropriate for another etching process. Consequently, in order to use the same apparatus for a different process, the user must change the gas distribution plate which results in expensive down time.
Accordingly, a need exists for an improved gas distribution plate that substantially reduces etching nonuniformities which occur between the center and edge of the semiconductor wafer using prior art gas distribution plates.
A gas distribution plate for a semiconductor processing chamber includes a gas distribution plate for distributing gases across a surface of a semiconductor wafer to be processed in the chamber. The gas distribution plates has a substantially planar member having gas outlet means for distributing a reactant gas across the surface of the semiconductor wafer, the gas outlet means includes a plurality of apertures defined in said planar member, the plurality of apertures having different areas at predetermined locations to adjust etching gas flow. A pumping means is provided for evacuating a reactant-product gas created across the surface of the semiconductor wafer during wafer processing. The pumping means includes a plurality of tubes extending through the planar member, the plurality of tubes having apertures, and the apertures have different areas at predetermined locations to adjust reactant gas and reactant-product gas flow wherein the gas outlet means and the pumping means coact to substantially maintain a predetermined concentration of the reactant gas and a predetermined concentration of the reactant-product gas across the surface of the semiconductor wafer during wafer processing.